# std::deque<T,Allocator>::insert

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< cpp‎ | container‎ | deque

iterator insert( const_iterator pos, const T& value ); | (1) |
iterator insert( const_iterator pos, T&& value ); | (2) | (since C++11)
iterator insert( const_iterator pos, size_type count, const T& value ); | (3) |
template< class InputIt > iterator insert( const_iterator pos, InputIt first, InputIt last ); | (4) |
iterator insert( const_iterator pos, std::initializer_list<T> ilist ); | (5) | (since C++11)

Inserts elements at the specified location in the container.

1) Inserts a copy of value before pos.
2) Inserts value before pos, possibly using move semantics.
3) Inserts count copies of the value before pos.
4) Inserts elements from range `[`first`,` last`)` before pos.

This overload has the same effect as overload (3) if `InputIt` is an integral type. | (until C++11)
This overload participates in overload resolution only if `InputIt` qualifies as LegacyInputIterator, to avoid ambiguity with the overload (3). | (since C++11)

If first and last are iterators into *this, the behavior is undefined.
5) Inserts elements from initializer list ilist before pos.

All iterators (including the `end()` iterator) are invalidated. References are invalidated too, unless pos ==`` `begin()` or pos ==`` `end()`, in which case they are not invalidated.

### Parameters

pos | - | iterator before which the content will be inserted (pos may be the `end()` iterator)
value | - | element value to insert
count | - | number of elements to insert
first, last | - | the range of elements to insert, cannot be iterators into container for which insert is called
ilist | - | std::initializer_list to insert the values from
Type requirements
- `T` must meet the requirements of CopyAssignable and CopyInsertable in order to use overload (1).
- `T` must meet the requirements of MoveAssignable and MoveInsertable in order to use overload (2).
- `T` must meet the requirements of CopyAssignable and CopyInsertable in order to use overload (3).
- `T` must meet the requirements of EmplaceConstructible in order to use overloads (4,5).
- `T` must meet the requirements of Swappable, MoveAssignable, MoveConstructible and MoveInsertable in order to use overloads (4,5). (since C++17)

### Return value

1,2) Iterator pointing to the inserted value.
3) Iterator pointing to the first element inserted, or pos if count == 0.
4) Iterator pointing to the first element inserted, or pos if first == last.
5) Iterator pointing to the first element inserted, or pos if ilist is empty.

### Complexity

1,2) Constant plus linear in the lesser of the distances between pos and either of the ends of the container.
3) Linear in count plus linear in the lesser of the distances between pos and either of the ends of the container.
4) Linear in std::distance(first, last) plus linear in the lesser of the distances between pos and either of the ends of the container.
5) Linear in ilist.size() plus linear in the lesser of the distances between pos and either of the ends of the container.

### Exceptions

If an exception is thrown other than by

- the copy constructor of `T`,

the move constructor of `T`, | (since C++11)

- the copy assignment operator of `T`,

the move assignment operator of `T`, | (since C++11)

this function has no effect (strong exception guarantee).

If an exception is thrown when inserting a single element at either end, this function has no effect (strong exception guarantee). Otherwise, if an exception is thrown by the move constructor of a non-CopyInsertable `T`, the effects are unspecified. | (since C++11)

### Example

Run this code

    #include <iostream>
    #include <iterator>
    #include <string_view>
    #include <deque>

    namespace stq {
    void println(std::string_view rem, const std::deque<int>& container)
    {
        std::cout << rem.substr(0, rem.size() - 2) << '[';
        bool first{true};
        for (const int x : container)
            std::cout << (first ? first = false, "" : ", ") << x;
        std::cout << "]\n";
    }
    }

    int main()
    {
        std::deque<int> c1(3, 100);
        stq::println("1. {}", c1);

        auto pos = c1.begin();
        pos = c1.insert(pos, 200); // overload (1)
        stq::println("2. {}", c1);

        c1.insert(pos, 2, 300); // overload (3)
        stq::println("3. {}", c1);

        // reset pos to the begin:
        pos = c1.begin();

        std::deque<int> c2(2, 400);
        c1.insert(std::next(pos, 2), c2.begin(), c2.end()); // overload (4)
        stq::println("4. {}", c1);

        int arr[] = {501, 502, 503};
        c1.insert(c1.begin(), arr, arr + std::size(arr)); // overload (4)
        stq::println("5. {}", c1);

        c1.insert(c1.end(), {601, 602, 603}); // overload (5)
        stq::println("6. {}", c1);
    }

Output:

    1. [100, 100, 100]
    2. [200, 100, 100, 100]
    3. [300, 300, 200, 100, 100, 100]
    4. [300, 300, 400, 400, 200, 100, 100, 100]
    5. [501, 502, 503, 300, 300, 400, 400, 200, 100, 100, 100]
    6. [501, 502, 503, 300, 300, 400, 400, 200, 100, 100, 100, 601, 602, 603]

### Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR | Applied to | Behavior as published | Correct behavior
--- | --- | --- | ---
LWG 149 | C++98 | overloads (3) and (4) returned nothing | returns an iterator
LWG 247 | C++98 | the complexity was only specified for inserting a single element | also specified for inserting multiple elements

### See also

emplace (C++11) | constructs element in-place (public member function)
push_front | inserts an element to the beginning (public member function)
push_back | adds an element to the end (public member function)
inserter | creates a std::insert_iterator of type inferred from the argument (function template)

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